This invention relates to a method of making a multiple necked can body, and more particularly to a method of reforming at least a portion of a multiple necked-in portion to provide at least an essentially right cylindrical-shaped portion adjacent the last necked-in portion.
Methods of making two-piece cans by combining a drawn and ironed can body with a circular can end are well known. In these methods, the can user fills the can body and then typically attaches the can end to the can body by a method known in the trade as double seaming. With the ever-increasing use of such cans, particularly for packaging beverages, there has been an intensive effort made by the manufacturer to reduce the weight or amount of material in the can.
One such effort has been in the direction of reducing the amount of metal in the can end by reducing the diameter of the open end of the can body which results in using less metal in the can end. The process of reducing the diameter of an open end of a tubular body is known as necking and is accomplished generally by one of two methods. In a spin-form method, the tubular body, such as a can body, for example, is placed upon a rotating mandrel and as the can body rotates, a tool is impinged against the periphery of portion of the body to be necked in. The tool is advanced inwardly toward the axis of the can body along an arc of predetermined radius until the desired reduction in diameter is achieved. In a push-form method, the closed end of the can body is mounted in a fixture in axial alignment with a female forming die. By axial movement of either the fixture or the forming die, the can body is moved into the forming die which is configured to neck a portion of the open end of the can body by forming the metal along an arc of predetermined radius until the desired diameter is reached.
In either method there are limits as to the amount of diameter reduction that can be made in a single necking operation because the inward forming puts the metal in compression. Since the metal being formed in a can body is relatively thin, only a slight reduction in diameter can be made without causing the metal to wrinkle along the formed surface.
It has been discovered, however, that by making separate, sequential necking steps, a far greater reduction in diameter can be made without wrinkling than if the necking were done in a single step. This discovery has led to methods known as multiple necking and further categorized by the number of necking steps employed, double necking and triple necking, for example. Multiple necking produces a portion, extending upwardly from a lower cylindrical portion of the can body, comprised of segments having progressively smaller diameters stacked one on another. The axial extent of such portion is commonly referred to as the stack height. An essentially right cylindrical portion extending upwardly from such segmented portion to the flange of the can body is commonly referred to as the neck.
Although multiple necking is advantageous to achieve a maximal reduction in diameter and thus lessen the amount of metal required to make a can end, some disadvantages are introduced as well. For example, in a can of a given length, having a portion of the can of reduced diameter obviously decreases the volume available for the can contents. It is desirable, therefore, to keep the total extent or axial length of the necked-in portion, including the neck, to a minimum. This means that in each separately necked-in portion the smallest forming radius possible that can be used without wrinkling the metal should be employed, and the necked-in portion of the can should be confined to the smallest possible portion of can length adjacent the can end to be closed by double seaming. In the view of at least some packagers of carbonated beverages, however, the slightly rippled appearance resulting from necking to produce a multiple necked can detracts from the aesthetics of the package. Furthermore, some packagers of carbonated beverages believe that maximizing the neck length of a multi-necked can is advantageous in applying a commonly used multi-pack plastic carrier adjacent the ends of the cans.
Heretofore, in providing a multiple necked can, it has been considered desirable to minimize the extent of the neck immediately adJacent the can bead because it was believed that the overall length of the necked-in portion would necessarily have to be increased for each added increment of neck. It may be seen that increasing the overall length by adding to the neck, without altering the configuration of the necked-in portions below the neck, would either necessitate an overall increase in the length of the can or lower the position on the can at which the multiple neck forming operation is begun. Neither of these alternatives is considered to be desirable in a multiple necked can.
It would be desirable, therefore, to provide a method for making a multi-necked can body having a longer neck adjacent the annular bead of the double-seamed end without increasing the overall length of the necked-in portion of the can body.